(Updates with Frontex saying none of its staff involved)

VALLETTA, Oct 24 (Reuters) - A light aircraft crashed after taking off from Malta's main airport early on Monday, killing all five people on board, officials there said, in the island nation's worst peacetime air accident.

Airport sources initially said the plane was believed to be carrying officials from European Union border agency Frontex. But the organisation later said none of its staff was involved.

A military source at Malta International Airport said all five victims were French, though the French foreign ministry said it could not yet confirm that.

Television footage showed flames rising from wreckage near the runway, sending thick black smoke into the sky.

Staff said investigations had begun and the aerodrome was closed until further notice. Several flights have been diverted to Sicily, many delayed and some cancelled.

The twin-prop Fairchild Metroliner crashed at about 0520 GMT, the airport said.

"We can confirm that no European Union officials were on board. The plane also was not related to any of the European Union's activities," an EU spokesperson said.

Airport officials told Reuters the plane had been heading for Misrata in Libya.

(Reporting by Chris Scicluna; Additional reporting by Agnieszka Barteczko in Warsaw, Ingrid Melander in Paris and Phil Blenkinsop in Brussels; Writing by Isla Binnie; Editing by Andrew Heavens) ((isla.binnie@thomsonreuters.com; +39 06 8522 4392; Reuters Messaging: isla.binnie.thomsonreuters.com@reuters.net))

Keywords: MALTA CRASH/